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nmdm - nullmodem terminal driver
The nmdm driver provides two tty(4) devices connected by a virtual “null
If either of the two tty devices have the CDSR_OFLOW bit (“stty dsrflow”)
set in their line discipline, the nmdm device will emulate the speed
configured in the termios(4) settings. The speed emulation works
independently in the two directions, controlled by the slower end’s
termios settings (c_ispeed, c_ospeed, CS5 ... CS8, CSTOPB and PARENB).
/dev/nmdmN[AB] nullmodem device nodes. Where the A node has a matching
The nmdm driver implements “on-demand device creation” so simply
accessing a given instance in /dev will create it.
stty(1), termios(4), tty(4)
The nmdm driver first appeared in FreeBSD 4.4.